The invention relates to the definition and the exploitation path of a Medium Access Control (MAC) protocol to be applied in wideband point-to-multipoint transmission systems, that rely on optical physical layer (Passive Optical Network) or radio physical layer and operate according to the time division multiple access schema and ATM transport format.
Among access techniques in telecommunication networks, point-to-multipoint on radio or physical channel are having a great market success due to their indubitable advantages in terms of flexibility and costs compared to point to point solutions.
As well known by skilled in the art, this kind of systems is characterised by the presence of a Master Station (MS) and a certain number of Peripheral Stations (PS): downstream channel (from MS to PS) is broadcast while upstream channel (from PS to MS) is used with time division multiple access (TDMA) under MS control.
To properly realise transmission from many PS to the single MS on a single channel, a point-to-multipoint system needs a solution to allow effective sharing of the single communication channel and to avoid that each PS transmission could interfere with others'.
The solution for physical mean sharing is generally based on time division multiple access, that is the single communication channel used for transmission from PSs to MS is divided into time slots defined on the basis of timing diffused on the broadcast downstream channel.
Each time slot is reserved to transmission from a single PS that is activated in that particular slot by a message, called ‘grant’, sent by the MS on the downstream channel.
MAC functionality, located in the MS, is in charge of generating these ‘grant’ messages in order to satisfy bandwidth requirements of PSs.
In an ATM system, moreover, MAC functionality has to be able to guarantee that bandwidth assigned to each PS allows to fulfil quality of service parameters of each connection belonging to different classes of traffic defined in the international specifications.
In specialised literature and patent specifications various TDMA solutions have been proposed; they can be divided into two categories:                extremely specialised ones, based on physical channel properties and little reusable even in different versions of the same equipment; these solutions are often enough simple, still being very sensitive to round trip delay, channel capacity and error probability.        flexible solutions, very complex in hardware but with indubitable advantages of total adaptivity.        
We can quote some of the most interesting experiences about these techniques. In the CEE financed project “RACE 2024 Broadband Access Facilities” an experimental system to access a passive optical network has been implemented. In this system the MS (optical line termination) manages upstream channel by the generation of ‘grants’ dedicated to single users connected to peripheral stations. Complexity was high due to the exchange and treatment of queue status and the system was not able to optimise transportation of ATM connections carrying narrowband services like, for example, telephone calls.
A different approach, taking into account narrowband services, was based on a MAC protocol that allowed allocation of the bandwidth to services on a semi-permanent basis, but unfortunately treated in the same manner also variable traffic or wideband connections, like, for example, Internet access connections.
Technique described in the Italian patent 01286424, titled “Metodo di gestione dell'accesso ad una rete ottica passiva (PON) in un sistema PON di tipo TDMA”, introduced major improvements in comparison with previous techniques allowing narrowband and broadband traffic treatment and, as far as broadband traffic is concerned, giving the possibility to allocate bandwidth in dynamic fashion.
These results have been achieved with some new concepts:                Use of ‘grants’ addressing PS and not the user flux with the advantage of letting the PS choosing which user (connection) to serve each time that a grant is received.        Narrowband and constant bandwidth broadband traffic treatment via a semi-permanent table.        Variable bandwidth broadband traffic without maximum delay requirements is treated with an algorithm that takes into account the fullness level of queues in the PS to decide PS priority for ‘grant’ assignment.        